Compression and tensile testing of electrodeposited nickel films with micro-sized specimens were reviewed. Preparation of micro-specimens without the tapering was realized by the micro-specimen fabrication method developed in our group. Accurate micro-testing method with precisely-shaped specimens is needed to reveal micro-mechanical properties of electrodeposited metals. The micro-testing on nanocrystalline nickel plated by an electrodeposition method with supercritical carbon dioxide showed remarkably high strength, and the strength increased with a decrease in the specimen size. The results indicated grain boundary mediated deformation of the electrodeposited nanocrystalline nickel.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 7–12.

Young's modulus (E), shear modulus (G), bulk modulus (K) and Poisson's ratio (ν) of Ti-Zr binary alloys containing 20, 40, 50, 60, 70 and 80 at% Zr and component pure metals (Ti, Zr) prepared by arc-melting followed by solidification process were determined precisely by ultrasonic sound velocity measurements. X-ray diffraction analysis showed that all the as-solidified alloys and pure metals were with a single-phase structure of the hexagonal close-packed lattice (martensitically formed α′-phase). The alloying addition of Zr to Ti effectively decreased both E and G values with their minimum values of 89.5 ± 1.0 GPa and 33.3 ± 0.4 GPa, respectively, being recorded at the same composition Ti-60 at% Zr. On the other hand, K values decreased slightly when the concentration of Zr was increased from 20 to nearly 50 at% and further increases in Zr concentration did not change K values greatly. The observed variations of Young's modulus with Zr concentration in the entire range of composition were well interpreted in terms of density (ρ), Debye temperature (θD) and concentration of atoms (n) in each alloy. The quantity ρθD2n−2/3 was revealed to be a good measure in predicting the tendency of variations of Young's modulus with composition in this binary system.

In spinal fixation devices, the activity of the patient can cause fretting of the metal-to-metal contacts between the rod and plug, which may result in failures. In this study, compressive fatigue tests were conducted with rods made of Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) with oxygen contents of 0.06 mass% (06O) and 0.89 mass% (89O) and Ti–6Al–4V extra low interstitial alloy (Ti64) as comparison in both air and saline solution. The fatigue strength increases in the order of 06O < 89O < Ti64 in both air and saline solution. These results indicate that solid-solution strengthening by oxygen improves the fretting fatigue resistance of the TNTZ rod.

Anisotropy of the Young's modulus and microstructure of a recrystallized β Ti-Mo-Al-Zr alloy with a Goss texture were investigated. Specimens were solution-treated at 1173 K for 3.6 ks after cold rolling with a reduction rate of 99%. The {011}<100> Goss recrystallization texture developed as a major texture component. The Young's modulus was evaluated by tensile tests using a strain gage method. Anisotropy of the Young's modulus depending on the loading direction was observed: The lowest and highest values of the Young's modulus were 44 and 77 GPa, respectively. The compliance anisotropy factor, J, and the characteristic modulus, S11, of the alloy were calculated from the measured Young's moduli and the volume fractions of the texture components.

Porous materials show low Young's moduli and excellent bonding to living bone. However, the strength of such materials is often insufficient in the initial stage of implantation. Thus, the objective of this study was to increase the strength of porous titanium by filling the pores with polyglycolide (PGA), a biodegradable plastic. PGA powder was prepared via the thermal decomposition of sodium chloroacetate at 433 K. The PGA was then introduced into the pores of porous Ti (porosity: 60%) using two methods: (i) centrifugal packing and heating and (ii) heat injection. In the latter method, almost all pores were filled by PGA; the filling fraction was measured to be 65–85% regardless of the injection temperature. When the pores in the porous Ti were filled with PGA, the compressive strength increased drastically from 40 to 100 MPa. The increased strength is comparable to that of cortical bone. In addition, the strength increased with increasing injection temperature. In an animal test, unfavourable autopsy findings, such as suppuration, bleeding, and hyperplasia of the connective tissue, could not be confirmed in rats and no bone was observed in the pores of the Ti–PGA composite. Decomposition of PGA lowered the surrounding pH, it was found to inhibit bone formation in the pores of the porous Ti. It is important to control the decomposition rate of PGA.

We studied the fabrication of a TiO2/SiO2 composite coating on Ti. At a temperature above 1100 K with oxygen partial pressure, a self-organized coating of rutile phase TiO2 is formed on a Ti substrate. The thick TiO2 coating (> 10 μm) had a “piecrust-like” multilayer structure, which comprise TiO2 monolayers and gaps. A composite coating containing SiO2 was fabricated via a sol-gel method in vacuum to improve the exfoliation strength of the brittle, porous TiO2 coating. Cross-sectional SEM images revealed sufficient amounts of SiO2 in the gaps between the TiO2 monolayers in the TiO2/SiO2 composite coating, even at the interface between the oxide coating and the substrate. Exfoliation stress of the composite coating was up to 10–15 times higher than for the self-organized TiO2 coating alone, and the composite coating's failure mode was interfacial compared with cohesive for the self-organized TiO2 coating.

Ti-15Zr-7.5Mo alloy was melted and its structure and mechanical properties were evaluated, followed by micro-arc oxidation (MAO) treatment to add bioactivity. Melted Ti-15Zr-7.5Mo alloy was consisted of mainly β containing of metastable α'' and ω phases. The Vickers hardness of the alloy was 420 HV and larger than those of Ti-6Al-4V alloy (320 HV) and Ti-29Nb-13Ta-4.6Zr ally (TNTZ) (180 HV). The Young's modulus of the alloy was about 104–112 GPa and almost the same as that of Ti-6Al-4V alloy (113 GPa) and larger than that of TNTZ (80 GPa). The MAO treatment was performed in a mixed electrolyte of 0.1-mol L−1 calcium glycerophosphate and 0.15-mol L−1 calcium acetate with a positive maximum voltage of 400 V and a 31.2 mA cm−2 for 600 s. Porous composite oxide of Ti, Zr, and Mo containing large amounts of Ca and P was formed on Ti-15Zr-7.5Mo alloy by micro arc oxidation (MAO) treatment. Zr was preferentially enriched and Ti and Mo were depleted in the oxide layer. Pore size was larger than that of CP Ti. The ability of calcium phosphate formation of the alloy in Hanks' solution after MAO treatment was less than those of CP Ti and TNTZ. It is necessary for the alloy to conduct a chemical treatment to accelerate bone formation.

The susceptibility to environment-assisted cracking (EAC) of super-elastic TiNi alloy was investigated as a function of the electrochemical potential and solution pH. The investigation was conducted using a slow-strain-rate tensile test apparatus with a potentiostat. The test solutions were sulfate solutions with various pH values adjusted by H2SO4 or NaOH. The alloy deforming under cathodic reaction fractured under the relatively small strain where the alloy was in the stress-induced martensitic phase. A larger EAC susceptibility was obtained at lower potential and lower pH, which indicates that this is a general feature of hydrogen embrittlement. The severe EAC region of TiNi alloy was different from that of TiAl alloy. The EAC susceptibility was strongly correlated with the cathodic charge density, irrespective of the pH or potential: a charge density below 0.025 MC m−2 yielded almost no EAC; however, above 0.025 MC m−2 EAC was induced, and the EAC susceptibility was independent of the charge density. Hydrogen in solid-solution state was detected in the alloy at a charge density below 0.025 MC m−2, and hydride started to form at a density above 0.025 MC m−2.

Air-formed surface oxide films on four types of Co-Cr- alloys were characterized using X-ray photoelectron spectroscopy (XPS) and five types of Co-Cr alloys were anodically polarized, to identify the effects of the addition of N, Mo, and W to Co-Cr alloys containing high Cr on the surface composition and corrosion resistance. Co-20Cr-15W-10Ni (ASTM F90), Co-30Cr-6Mo, Co-33Cr-5Mo-0.3N, and Co-33Cr-9W-0.3N were employed for XPS and the above four alloys and another Co-30Cr-6Mo (ASTM F75) were employed for anodic polarization. The surface oxide film on the Co-Cr alloys consisted of oxide species of Co, Cr, Mo, W and/or Ni contains a large amount of OH− with a thickness of 2.6–3.2 nm. Cations existed in the oxide as Co2+, Cr3+, Mo4+, Mo5+, Mo6+, W6+ and Ni2+. Cr and Mo are enriched and Co and Ni are depleted in the surface oxide film. W was enriched in the case of Co-20Cr-15W-10Ni but depleted in the case of Co-33Cr-9W-0.3N. On the other hand, Cr, Mo, W and Ni were enriched and Co was depleted in the substrate alloy just under the surface oxide film in the polished alloy. During rapid formation of the surface oxide film, Cr was preferentially oxidized and the oxidation of Co and Ni delayed, according to the oxidation and reduction potentials of these elements. The Co-Cr alloys essentially have high localized corrosion resistance that is not easily affected by a small change of composition. Co-33Cr-5Mo-0.3N shows higher corrosion resistance compare than conventional Co-Cr alloys.

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are used for biomedical implants such as artificial joints because they have excellent wear and corrosion resistance and biocompatibility. Electron-beam melting (EBM) is a type of additive manufacturing technique for metals. We used EBM to fabricate 20 rods of a Co-Cr-Mo alloy with height of 160 mm arranged in a 4 × 5 matrix and observed the phase constitution in the middle part (at a height of 80 mm) of the rods by scanning electron microscopy-electron backscatter diffraction. We found that the rods in the center part of the matrix consisted of more of the face-centered cubic (γ) phase and less of the hexagonal close-packed (ε) phase than rods in the outer part. This happened because even though each rod was fabricated under the same beam condition, the rods at the center had been exposed to higher temperature than those in the outer part, and less thermal dissipation took place because the neighboring rods were also heated by the electron beam. This difference in the thermal histories should be taken into consideration when many objects are fabricated simultaneously.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 63 (2016) 10–16. Figure 4 and Fig. 6 were changed for more clear and appropriate explanation.

Changes in the microstructure and hardness of biomedical Co-Cr-Mo forged alloys (Co-27Cr-6Mo-0.77Si-0.64Mn-0.17N-0.06C (mass%)) during aging were investigated with a focus on precipitation. After solution treatment at 1523 K for 1.8 ks, the alloys were subjected to aging at temperatures between 973 and 1373 K for up to 86.4 ks. η-phase (M6X-M12X type), M23X6-type and π-phase (A2T3X type) precipitates were detected after aging. The formation of π-phase precipitates was detected in alloys aged between 1023 and 1123 K for holding times ≥ 21.6 ks, with a nose temperature between 1073 and 1123 K. The presence of π-phase precipitates in the aged Co-Cr-Mo alloy is reported for the first time; N contained within the alloy is believed to contribute to formation of the π-phase. The formation of a hexagonal-close-packed Co-based metallic phase (ε-phase) was observed between 1023 and 1123 K. The Vickers hardness increased in alloys aged at 1023 and 1073 K. This increase in hardness is attributed to the presence of π-phase and ε-phase and their wide-area precipitation.

Pin-on-disk wear tests using Co-Cr-Mo (CCM) alloy pins and disks were conducted in 0.14 M NaCl solutions with and without albumin. To clarify the effect of precipitates in the CCM alloys on the alloy wear behavior, as-received (having precipitates) and solution-treated (having no precipitates) CCM alloys were used as specimens. Friction coefficients during wear testing were measured. After the wear testing, the mass loss of pins and disks, wear tracks on the disks, and the wear debris were examined using scanning electron microscopy (SEM) and laser microscopy (LM). The concentration of metallic ions in solution was analyzed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). In the solution without albumin, the friction coefficient increased with increasing sliding time and discontinuous wear grooves with attached and detached sections were observed, indicating that adhesive wear was dominant. On the other hand, in the solution with albumin, the friction coefficient was constant independent of the sliding distance and continuous wear grooves were observed, indicating that abrasive wear was dominant. High amounts of mass loss were detected from the as-received alloys in the albumin solution, and it is theorized that the wear debris (including precipitates) enhanced the third-body wear. The concentration of Cr ions in solution was lower than the expected values based on the alloy composition. In the solution with albumin, it was thought that the Cr ions bonded with the albumin, increasing the amount of available Cr ions in solution.

The microstructure and mechanical properties of thermomechanically processed Zr-14Nb alloy with low magnetic susceptibility were investigated in this study. The stress-strain curves of Zr-14Nb alloy were classified as higher or lower work-hardening types depending on the thermomechanical process. Serration was observed in curves of the higher work-hardening type. SEM-EBSD analysis indicated that {332}<113> twinning should form at the bands that appear after tensile testing. On the other hand, no serration appeared in the lower hardening rate curves. The mechanical properties of centrifugally cast Zr-14Nb alloy with a lower work-hardening rate possessed moderate tensile strength and high elongation because of the formation of the isothermal ω phase during cooling after centrifugal casting, although the tensile strength was increased and the elongation was decreased with increase of the isothermal ω phase formed after aging. The magnetic susceptibilities of thermomechanically processed Zr-14Nb alloys were still one-third lower than those of Ti-6Al-7Nb. Accordingly, the mechanical properties of Zr-14Nb can be controlled by thermomechanical processing while keeping low magnetic susceptibility.

In this study, we evaluated the osseoconductivity of Type 316L stainless steel with self-organized nanopores of three different average diameters (26, 90, and 177 nm), formed by anodic polarization. The proliferation, alkaline phosphatase activity, and morphology of MC3T3-E1 mouse osteoblast-like cells, cultured on the self-organized nanopores were evaluated. The cell densities on samples with the nanopores were higher than those on mechanically finished surfaces that were mirror-polished or ground with #2000 SiC paper. In particular, the highest cell density and alkaline phosphatase activity were obtained on the nanoporous sample with the smallest diameter of 26 nm. Cells on the samples with 26 nm nanopores extended further and spread more filopodia compared with cells on samples with the other surface morphologies. Therefore, we concluded that self-organized nanopores with an optimal diameter (e.g., 26 nm) on Type 316L stainless steel could enhance long-term cell activity.

ZnO-CaO-P2O5-Nb2O5 invert glasses, with ZnO substituted for CaO, were successfully prepared using a melt-quenching method. Their structures, dissolution behaviors, and antibacterial abilities were evaluated. Niobate switched its role of network former to modifier with increasing ZnO content, as Zn2+ ions preferentially coordinated with phosphate groups. In parallel, with increasing content of ZnO in the glasses, P-O-Zn bonds were formed, which crosslinked phosphate groups with ZnO acting as a network former. As a result, the glass-forming ability and chemical durability of the glasses were improved. The glasses showed antibacterial ability to gram-positive and -negative bacteria.

Fig. 5 Number of E. coli (left) and S. aureus (right) after cultivation with the glass powders for 24 h. “0 h control” means the seeded number of E. coli and S. aureus, and the error bar means standard deviation.
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Breast cancer is highly metastatic to bone tissue and causes osteolytic lesions through osteoclast activation. Although the effects of osteolytic metastasis on bone quantity have been well studied, whether osteoclast activation induced by cancer bone metastasis affects the bone microstructure, a notable aspect of the bone quality, remains uncertain. The aim of this study was to clarify the effect of osteolytic bone metastasis in breast cancer on the microstructure of the bone matrix, particularly the integrity of collagen fibril orientation. Osteolytic breast cancer cells induced hyperactivation of osteoclasts both in vivo and in vitro. Osteoclasts differentiated by culture of monocytes in the cancer cell-derived conditioned medium had an increased number of nuclei; more specific podosome structures were organized compared to osteoclasts differentiated in the control medium. These observations suggest that the resorptive capacity of a single osteoclast was abnormally upregulated in the cancer-involving environment, causing geometrically irregular resorption cavities. Histological studies on mouse femurs with metastasis of breast cancer MDA-MB-231 cells revealed that the osteoclasts in the metastatic bone were abnormally large and they generated resorption cavities that are irregular both in size and in shape. Notably, collagen matrix in newly formed bone in metastatic bone exhibited a significantly disorganized architecture. To the best of our knowledge, this is the first report demonstrating that osteolytic bone metastasis induces the disruption of bone matrix alignment, which determines the mechanical function of bone in both intact and diseased bone tissue.

Selective abnormal growth behavior of Goss grains was investigated by interrupting secondary recrystallization process in magnetostrictive (Fe83Ga17)99.9(NbC)0.1 rolled alloy sheets. The evolution of microstructure and texture was analyzed by electron back-scattered diffraction while ramping the temperature from 1123 to 1353 K. The results indicate that before temperature increasing up to 1203 K, Goss grains had no advantages in size and quantity, and the abnormal grain growth did not occur. Goss grains grew abnormally from about 1218 K due to the inhibitory action of Nb-rich precipitates on normal growth of other orientated grains. The γ-fiber texture was the predominant texture before the onset of secondary recrystallization. When the secondary recrystallization got fully development, a sharp Goss texture and an average magnetostriction up to 210 ppm were obtained in the sample annealed at 1353 K.

A method to build an image-based model from a high-resolution X-ray CT image has been proposed for crystal plasticity finite element (CPFE) analysis in this study. The grain microstructures of aluminum alloy were captured by X-ray CT in synchrotron radiation facility, SPring-8. An image-based model of crystallographic grains was reproduced by the proposed method, and the model was analyzed by CPFE. By this, it was represented that deformation analysis of a polycrystal microstructure considering actual grain shapes was available suggesting that the deformation mechanism would be made clear by the image-based CPFE with further work.

The creep rupture strength and the degradation mechanism of 23Cr-43Ni-7W alloy weld joints were investigated using creep rupture tests and microstructure observation of the ruptured specimens. The creep rupture tests were conducted at 973, 1023, and 1073 K at stresses from 80 to 180 MPa. The creep strength of the weld joints was higher than that of the base metal. The ruptured area of every specimen was over 10 mm away from the bond line. The microcracks increased gradually up to 10 mm from the bond line, beyond which they suddenly increased. In the grains, traces of M23C6 were observed near the bond line, and the sizes of the M23C6 deposits increased further away from the bond line. But the size of the Laves phase was constant in every observed area. On the grain boundary, the grain boundary shielding ratio by precipitates was constant until 10 mm from the bond line, beyond which it decreased. These observations show that the creep strength near the bond line is higher than that of the base metal because of both precipitation strengthening in the grain and grain boundary.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 79 (2015) 348–355.

This study examined the delaying effect of fatigue crack growth induced by high-density electric current on A6061-T6 aluminum alloy. To investigate the effect, fatigue tests were conducted using specimens with and without electric current treatment. The fatigue life of the treated specimens increased significantly compared with untreated specimens. After the tests, the fracture surfaces were examined using scanning electron microscope. In the specimens in which electric current was applied, local melting on the crack surface was observed via fractography. To clarify the effects of electric current treatment on fatigue crack propagation, early crack growth was investigated using the plastic replication method. A delaying effect was particularly noticeable in the small-crack region. Results show that this delaying effect can be attributed to crack shielding caused by local melting on the crack surface, which signifies that the fatigue life is improved by the application of high-density electric current.

Fe-Cr based soft magnetic alloy, which has excellent soft magnetic properties and practical corrosion resistance is required. SUS430L is one of the candidate Fe-Cr based alloys with soft magnetic property in stainless steels. To improve soft magnetic properties, sintering process is useful to make low Cr alloy by adding the pure iron powder to SUS430L powder. While, reduction of Cr content expected to deteriorate corrosion resistance of the alloys. To evaluate the effect of Cr content on mechanical and electrochemical properties of the soft magnetic alloys, sintered SUS430L based alloys with different Cr content were prepared using metal injection molding process. We carried out slow strain rate tensile (SSRT) test and open circuit potential (OCP) to evaluate their mechanical properties and electrochemical properties. The results of SSRT and OCP suggest that Cr content enhance stress corrosion cracking. OCP value was affected formation of passive film on elastic deformation and collapse of it on plastic deformation during SSRT test.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 63 (2016) 291–297.

The alloying effect of Mo on the seawater immersion corrosion for low alloy steel was investigated using weight loss tests and electrochemical impedance spectroscopy (EIS) in seawater. The Mo-containing low alloy steel showed an excellent corrosion resistance by the long immersion test due to the formation of homogeneous rust layer preventing active dissolution. SEM and XPS analyses were conducted to observe cross-sectional images of rust layer and indentify chemical composition of oxide formed on the surface after immersion test. The results revealed that the MoO42− ions which were oxidized from Mo form the compounds which disturb the approach of aggressive ions.

Uncontrolled waste marble powder contributes negatively to the environment. This paper reports a cheap and facile method to prepare a super-hydrophobic self-cleaning coating with high-robustness by using waste marble powder as the basic components. The PFOTES (1H,1H,2H,2H-Perfluorooctyltriethoxysilane) was selected as the modification agents which is self-assembled on the marble powder surface. A very low mass concentration of PFOTES (0.1208% wt.) increases the water contact angle of a coated sample from 11.3° to 138°. With the gradual increase of PFOTES, the water contact angle increases from 138° to 153°. The sliding angle value, however, varies from over 180° (the water droplet will not fall even it is turned upside down) to 6.8°, which represented the wetting model changing from Wenzel model to the Cassie-Baxter model. Thus, the super-hydrophobic self-cleaning coating is obtained. Besides, the coating showed an excellent robustness, no obvious contact angle and sliding angle differences were detected after 10 times' robustness test (the contact angle and sliding angle ranged from 147° to 155° and 6.8° to 8.5° respectively).

High Silicon Solid Solution Strengthened Ferritic Ductile Cast Iron possesses advantages, such as better combination of strength-elongation, higher fatigue strength, smaller section thickness sensitivity, higher machinability etc., over conventional ferrite-pearlite type ductile cast iron. However, industrial application of high Si ductile cast iron is still very limited, because of the lower Charpy impact value at room temperature. As the toughness of iron strongly depends on the strain rate as well as temperature, dynamic three-point bending tests are conducted on 3～4%Si ferritic ductile cast iron at stroke speed of 10−3～102 mm/s, and at −20～22℃. The relations of the crack initiation energy Ei, the crack propagation energy Ep, the total absorbed energy Et and the maximum bending stress σb,max to the strain rate show abrupt dropping of these characteristic values at critical strain rate, depending on silicon content and test temperature. σb,max keeps increasing with increasing strain rate $\dot{\varepsilon}$ as far as the fracture origin is ductile, it slightly decreases over $\dot{\varepsilon}_\sigma = \dot{\varepsilon}_{fD}$ where the dimple fracture completely disappears. σb,max, Et and Ei of each silicon iron is well expressed in relation to strain rate-temperature parameter R, T ln(A/$\dot{\varepsilon}$). The critical R values for Et, Ei, and σb,max (Rt, Ri and Rσ) decrease linearly with decreasing the silicon content of iron. The critical value for σb,max (Rσ) is lowest, indicating Rσ gives a wider design tolerance.

25 vol% Ni electroless-plated FeB powders were consolidated by spark sintering for the development of hard materials. The sintering curves of the FeB–25Ni powders were between those of as-received FeB without Ni addition and pure Ni powders. The maximum densification rate in the FeB–25Ni was achieved at an apparent relative density of 0.79, which was higher than that of the as-received FeB (0.6) and close to that of pure Ni (0.74). The densification of FeB–25Ni was predominantly a result of plastic deformation and power-law creep deformation of the Ni binder. The change in densification mechanism occurred roughly at the maximum densification rate. The sintering curve and densification rate of the FeB–25Ni powders could be explained by the combination of sintering curve and densification rate obtained from the as-received FeB and pure Ni powders. The increase in maximum holding temperature led to the improvement in hardness and compressive and fracture toughness properties, which resulted from the increase in apparent relative density due to the activation of diffusion at the interfaces between particles.

For the establishment of appropriate recycling process, the delamination of electric components from printed circuit boards (PCBs), which are major components of e-waste, is expected, because some of useful critical metals are concentrated in specific components. However, the knowledge about the mechanism of the delamination process in a drum typed agitation mill is still limited and uncertain. To better comprehend the mechanism, in this study, the particle-based simulation and comminution tests using handmade PCBs were conducted. The behavior of PCBs and the air flow in the mill having flexible chains was simulated by the discrete element method (DEM) coupled with computational fluid dynamics (CFD). To model the shape of PCBs, the particle based rigid body model was introduced into the DEM. Since this model could not directly simulate the breakage phenomena, collision energy was calculated to qualitatively evaluate the comminution performance. In addition, the simulation results were compared with the experimental comminution tests. This study demonstrated the behavior of PCBs and the air flow in the mill, and the effect of the air to comminution process in the mill. It was also shown that the collision energy related to parts collision was better correlated with the experimental results and this correlation can be assumed using first order rate equation, which suggested part detachment was mainly brought by direct collision to parts in the mill.

A Bi2Te3–Sb2Te3 solid solution was prepared by mechanical alloying (MA) followed by hot pressing (HP). X-ray diffraction indicated that all samples which were removed at a depth below the surface of approximately 1 mm were single-phase and isotropic Bi2Te3–Sb2Te3 solid solution. Reduction of the phonon thermal conductivity as a result of the fine-grains caused by MA predominated over the solid-solution effect caused by melt growth. The Seebeck coefficient and electrical and thermal conductivities fluctuated between those for (Bi2Te3)0.15(Sb2Te3)0.85 and (Bi2Te3)0.2(Sb2Te3)0.8 at room temperature. A (Bi2Te3)0.15(Sb2Te3)0.85 solid solution with a dimensionless figure of merit ZT = 1.16 at 367 K was obtained by MA–HP. These results indicate that the maximum ZT of the Bi2Te3–Sb2Te3 solid solution obtained by MA–HP was not restricted to a composition of (Bi2Te3)0.25(Sb2Te3)0.75, which has the minimum phonon thermal conductivity in the case of melt growth.

Microcrystalline silica impurities such as quartz and opal-CT commonly associated in bentonite should be controlled and removed as far as possible when bentonite is used as biocompatible raw material because the impurities are hazardous in human health. Since opal-CT contained in Korean Ca-bentonite in trace amounts cannot be well separated by conventional sedimentation method, in this work, the ultrasound-assisted removal of the impurity was attempted. Irradiating ultrasound into bentonite-water suspension promoted the production of fine montmorillonite particles in the suspension and the production markedly increased when montmorillonite was activated by Na2CO3. Subsequent centrifugation of the suspension made it possible to recover pure montmorillonite particles as an overflow product. Only 16.2 mass% of total solids was recovered as an overflow from non-activated suspension, whereas 63.5 mass% was recovered from activated suspension at centrifuging speed of 10000 rpm. Increasing sonicating time enhanced the yield of overflow, however, excessive sonication up to 10 min hindered the high purification of montmorillonite. It was observed that the peak reflection of (101) plane of opal-CT in overflow increased as sonicating time increased during prolonged sonication.